1. Field of the Invention
The present invention relates to a method for producing an optical recording medium, particularly a chalcogenide suboxide film capable of being recorded and erased by laser light. More particularly, the invention relates to a method for producing an optical recording medium which is excellent in adhesive properties between an optical recording film and a substrate, which can maintain an optical recording characteristic for a long period of time and which is excellent in stability.
2. Prior Art of the Invention
Optical recording media so far known include a system for forming small holes or bubbles and a system for varying optical characteristics of a film by thermal energy of laser light. In the former system, at the time of recording, change in rugged shape occurs in the recording film layer and therefore the recording film or substrate tends to change in quality and corrosion with a lapse of time. Normally, two recording media have been used in the form of an air sandwich. On the other hand, in the latter, two recording media are merely used with said media bonded together, thus providing an advantage in that the producing step can be materially simplified. Among materials used for the latter, there is known a chalcogenide suboxide, particularly, a tellurium suboxide TeO.sub.x, as those having a high sensitivity, that is, a material which is great in change of optical characteristic with respect to the intensity of given incident light, the x used being 0&lt;x&lt;2.0. This material can be obtained in the form of a mixture of Te and TeO.sub.2. In this specification "suboxid" indicate the mixture. However, power of irradiated light may be varied to reversibly change the optical characteristic, whereby this material is being watched in respect of the fact that recording and erasing may be suitably repeated.
Known methods for producing tellurium suboxide films include a method comprising placing powder of TeO.sub.2 on a W or Mo boat type heater, and energizing the heater to effect Vacuum deposition while partially reducing the TeO.sub.2 ; a method comprising putting a mixture of TeO.sub.2 powder and various reduced metals into a quartz crucible to heat and deposit the same under vacuum phenomenon; and a method comprising using TeO.sub.2 and metal Te as a separate source of evaporation to deposit them simultaneously.
However, among these methods, the former two methods are simple but have a disadvantage in that since a reducing force of the boat or reducing metal is varied during the deposition, a change in composition in a direction of film-thickness of the deposited film tends to occur.
In the above-described method which used two deposition sources, the composition is not varied in the direction of film-thickness and a uniform film may be obtained. In the film produced by said method, one in which x of TeO.sub.x is x&lt;1 is low in darkening starting temperature and high in sensitivity whereas where it is left under a relatively high temperature below the blackening starting temperature and where it is left under high humidity, a change in permeability is great. Because of this, one which is poor in sensitivity but in the range of 1&lt;x had to be used mainly in view of stability of the film.
In addition, a thickness of the optical recording film had to be increased to compensate for deterioration of absorption of light. Furthermore, there also involved disadvantages in that the adhesive properties between the formed optical recording film and the substrate is not sufficient, and it is disengaged from the substrate during the manufacture or during the use.